Geert Kleinnibbelink

Exercise-Induced Cardiac Function under Hypoxia 2 53 DISCUSSION The aim of our study was to investigate the impact of a bout of high-intensity exercise under hypoxia versus normoxia on EICF on both ventricles. The main findings were 1) a bout of 45-minute high-intensity exercise induced a reduction in functional indices of right- and left-sided cardiac function andmechanics inhealthy individuals, 2) the reduction in right- and left-sided cardiac function was more pronounced when echocardiography was performed during a standardized low-to-moderate-intensity recumbent exercise challenge and 3) there was no impact of hypoxia on exercise-induced reduction in right- or left-sided cardiac function and mechanics, either under rest or under stress. Taken together, these data indicate that EICF after short-term high-intensity exercise is not exaggerated under hypoxia, suggesting that an additional cardiac load (induced by hypoxia) on the RV does not necessarily relate to an exaggerated EICF in this setting. High-intensity exercise-induced cardiac fatigue A bout of 45-minute high-intensity running exercise induced a reduction of both RV and LV function indicative for EICF, which was mainly expressed during a low-to-moderate- intensity exercise challenge (‘stress’) compared to resting conditions. Earlier studies primarily investigated EICF after prolonged exercise ( > 180minutes) 4, 27 , however, recent research has revealed a dose-response relationship between EICF and the duration and intensity of exercise. 14, 39 Our study adds the novel knowledge that EICF also occurs after relatively short periods of high-intensity exercise in both the RV and LV. Interestingly, in contrast to other short-term high-intensity EICF studies 10, 14, 39 , we showed also marked reductions in LV function which may be due to the different type of exercise (running vs. cycling). An explanation for our ability to detect EICF after a relatively short duration of exercise may relate to the post-exercise assessment of cardiac function during ‘stress’, i.e. low-to-moderate-intensity exercise Indeed, some of the indices for systolic function were primarily/only reduced when echocardiography was performed during the low-to- moderate-intensity exercise challenge. For example, a reduction in RVLS post-exercise was only apparent during the low-to-moderate-intensity exercise challenge ( Figure 4A ). We believe the echocardiography assessment under low-to-moderate-intensity exercise is more likely to detect EICF. The recovery phase post-exercise is associated with a change